Composite polymer materials are made by the addition of functional fillers or additives to polymer materials. Compared to unfilled polymers, composites typically have a lower cost and/or improved physical properties. Functional fillers can be melt processed with the polymers or, following extrusion, impregnated into, suffused onto, or coated onto fibers or films either during fabrication or as a post-treatment. Typically the amount of functional filler that can be impregnated, suffused, or coated is limited by undesirable changes in mechanical properties, cost, and/or excessive shedding of the filler.
Filtration systems for liquids and gases are examples of one application of composite polymer materials. Economical, effective fluid filtration is accomplished by functional fillers that are supported and are not allowed to shed into the filtrate stream. Functional fillers used for filtration include activated carbon, zeolites, and catalysts. Structured adsorbents incorporate functional fillers into a fabric-like or porous solid structure. These articles typically are composed of a binder and functional fillers. Care is taken when designing structured adsorbents to select the fillers and optimize the structure of the adsorbent to achieve the desired rate and capacity of adsorbance.
FIGS. 1A and 1B show, respectively, AQF™ and KX™ adsorptive filtration media of structured activated carbon. FIG. 1A shows AQF™ air filtration media 10 that includes two-component fibers 12 and activated carbon granules 14. Fibers 12 have an inner core made from one polymer and an outer surface made from a second polymer. The polymer on the outer surface has a lower melting temperature than that of the polymer used for the inner core. Fibers 12 are heated to soften the outer surface, and then powders such as activated carbon granules 14 are blown onto the fibers. The softened polymer on the fiber surface acts as an adhesive. Activated carbon granules 14 can be partly covered or blinded by the adhesive, and is not incorporated within a fiber. The loss of active surface on the filler material that results from the adhesive blinding the filler reduces the adsorption capacity. The relatively large particle size required increases mass transfer resistance because adsorption needs to take place inside the particle, rather than on the surface. This results in slower kinetics compared to the kinetics of a material with smaller particles and less blinding of active surface area. In the example shown in FIG. 1B, KX™ PLEXX™ water filtration media 20 include fibers 22 having surfaces to which activated carbon granules 24 are adhered by a binder material 26. Activated carbon granules 24 are trapped by a web of fibers. The structure of this material limits the rate and capacity of adsorption and exhibits limiting issues that are similar to those discussed above in the AQF™ media case.
FIG. 2 presents another example of current approaches to impregnating fabrics and filter media with granular activated carbon. FIG. 2 is a SEM image of Lydall water filtration media 30 having a randomly configured fibrous substrate. Activated carbon granules 34 adhere to the surfaces of fibers 36. As in the KX™ and AQF™ media examples, fibers 36 of the substrate are composed of polymer.
Chitosan, together with its derivatives (e.g., chitosan acetate or chitosan lactate), is reported to possess hemostatic and antimicrobial properties and has been incorporated into bandages as a procoagulant to arrest bleeding. Publications concerning hemostasis discuss different aspects of blood clotting and their mechanisms. A review article, Whank, Hyun Suk et al. Journal of Macromolecular Science, Part C: Polymer Reviews, 45:309-323, 2005, discusses the role of chitosan and chitosan derivatives in platelet adhesion and platelet aggregation leading to clot formation. Platelet adhesion and platelet aggregation are aspects of cellular mechanisms for mammalian blood clotting. Chitosan is a de-acetylated product of chitin (C8H13NO5)n, an abundant natural glucosamine polysaccharide occurring in the shells of crustaceans, such as crabs, lobsters, and shrimp. Chitosan is non-toxic and biodegradable.
U.S. Pat. No. 3,903,268 discusses impregnating surgical gauze or pads with a solution of chitin or chitin derivatives and applying fibers composed of chitin and chitin derivatives to a wound to promote healing. U.S. Pat. No. 5,900,479 discusses the preparation of chitosan solutions in the form of chitosonium ion complexes or chitosan salts that can be formed into fibers and other shapes as an intermediate step, and then heated to achieve a polyanionic polymer condensation reaction. A characteristic of this formulation is that condensed chitosan salts resist dissolution in aqueous solutions. U.S. Pat. No. 6,897,348 describes a multi-layered bandage in which hemostatic agents, such as chitosan, and antimicrobial agents are present either within or as a coating over one of the bandage layers. Chitin fibers are pulverized and either incorporated into a woven substrate or applied in powder form directly to the wound. U.S. Pat. No. 4,543,410 describes the incorporation of chitin derivatives into a cellulose sponge to form a hemostatic material. U.S. Pat. No. 4,572,906 describes a solution of chitosan and lactic acid mixed with gelatin to form a wound-adherent hemostatic film. In all of the articles described by these patents, the surface areas of the healing agents presented to the wound are limited to the coating of the agents applied to the surfaces of the supporting fibers.
U.S. Patent Application Pub. No. US2005/0137512 describes a wound dressing for controlling severe bleeding. The wound dressing is prepared by degassing a chitosan biomaterial solution by heating at vacuum pressure, freezing the chitosan biomaterial solution, removing water from within the frozen chitosan biomaterial by freeze drying, compressing the chitosan biomaterial to obtain a compressed sponge, and baking the compressed chitosan sponge at 80° C. for 30 minutes. The resulting article is substantially comprised of the active ingredient chitosan. The compressed chitosan sponge is brittle and tends to crack if wrapped around a curved body part of a patient, making it impractical for use as a bandage in some situations. Also, the article works best when there is dry or slightly moist tissue around the wound area because the article adheres to these areas. The article is difficult to apply successfully to an internal wound or to a severe and/or irregular shaped external wound. The dressing is water soluble and dissolves when exposed to a large volume of liquid, such as copious blood flow. If the dressing dissolves, it may fail to form a good seal over the wound and clot formation becomes problematic. The inability of wound exudates to penetrate the dressing is another common disadvantage to achieving hemostasis in these prior art examples.
A review article by Lawrence L. K. Leung, ACP Medicine, Hematology XII—Hemostasis, 2003, discusses an alternative blood clotting mechanism: the initiation of an “intrinsic cascade” by a negatively charged surface like glass. The intrinsic cascade process, in this context, relates to the polymerization of fibrinogen into fibrin, a blood protein that lends structure to a blood clot. The use of silica powder as a procoagulant is mentioned in U.S. Patent Application Pub. No. 2006/0034935 A1 and in Stucky, Galen D. et. al., Journal of the American Chemical Society, 128:8384-8385, 2006, in which porous glass beads with calcium, a known co-factor in the clotting cascade, are recognized as a contact activator for the intrinsic clotting cascade. However, neither of these publications addresses the problem of supporting and maintaining the powder or glass bead silica in place after introducing it to a wound. Therefore, in wounds exhibiting high bleeding rates, the silica may be washed away instead of remaining at the injury site.